Method and composition for the electrolytic etching of beryllium-copper alloys



United States Patent 3,445,355 METHOD AND COMPOSITION FOR THE ELECTROLYTIC ETCHING OF BERYLLIUM-COPPER ALLOYS Paul T. Woodberry, Reading,Mass., and Herman Koretzky, Poughkeepsie, N.Y., assignors toInternational Business Machines Corporation, Armonk, N.Y., a corporationof New York No Drawing. Filed July 15, 1966, Ser. No. 565,386

Int. Cl. C23b 3/02 US. Cl. 204-141 9 Claims The present inventionrelates to a method and electrolyte composition for electrolyticallyetching metal alloys. In particular, the invention is concerned with theelectrolytic etching of beryllium-copper alloys, especiallyberyllium-copper alloys containing cobalt in the form ofcobalt-beryllide.

Many beryllium-copper alloys contain cobalt. When such alloys areprecipitation-hardened, grains of the intermetallic compound cobaltberyllide are formed in a matrix of copper. The resulting two-phasedsystem is difiicult to smooth or polish by conventional electrolyticetching techniques. The major diificulty is that the anodic potentialsestablished at the surfaces of the two phases result in a preferentialdissolution of one of the phases. The other phase protrudes at surfacesand edges and this results in a rough surface, rather than the desiredsmooth surface.

Accordingly, the objective of the present invention is to provide anelectrolyte composition and method for smoothly etching beryllium-copperalloys, especially beryllium-copper alloys containing cobalt beryllide.

A further specific objective of the invention is to provide acomposition and method for electrolytically smoothing beryllium-copperalloys containing grains of copper beryllide.

The manner in which the above objectives and many other highly desirableobjects and advantages are achieved in accordance with the presentinvention will be apparent in view of the following detailed descriptionof preferred embodiments thereof.

In general, the present invention comprises anodically etching anarticle of a beryllium-copper alloy containing cobalt-beryllide grainsto provide a smooth surface on the article by connecting the article asanode in an electrolytic system including an electrolyte containing thefollowing constituents:

hydrofiuosilicic acid, H SiF ethylene glycol, hydroxylaminehydrochloride, isopropyl alcohol, and

2,2 diquinoline.

Hydrofluosilicic acid, considering, for example, a bath of about 105 ml.volume, comprises the major portion by volume of the composition,generally over 50% and usually on the order of about 60% by volume. Thehydrofiuosilicic acid is used as 30% by weight aqueous H SiF Ethyleneglycol is present in a substantial but minor proportion, generally onthe order of about 20% by volume of the composition. The hydroxylaminehydrochloride is present in a small amount, generally on the order of 1gm. and preferably about 0.5 gm. The 2,2 diquinoline also is present ina small amount, usually less than 1 gm. and preferably about 0.2 gm. andis dissolved in the isopropyl alcohol. The isopropyl alcohol is presentin minor proportions which may comprise about 20% by volume of thecomposition.

The anodic current density on the surface of the part etched with thiscomposition is preferably in the range "ice of from about 500 to 1000amperes per square foot (a.s.f.).

The invention will be more fully appreciated in the light of thefollowing example which illustrates a preferred embodiment of thecomposition.

EXAMPLE 1 A part of beryllium-copper alloy which has beenprecipitation-hardened to form grains of cobalt-beryllide in a matrix ofcopper was anodically connected in an electrolytic cell which alsoincluded a stainless steel cathode plate opposite the part. Anelectrolyte of the following formulation was introduced into the cell:

about 30 C. and a current density of 500 a.s.f. was applied for 30seconds. The pH of the electrolyte was maintained between 4 and 5. Asmooth surface was produced on the metal part.

The distribution of current over the surface of the partelectrolytically etched can be adjusted to effect overall uniformattack. This is accomplished by the use of shaped cathodes, currentshields and current thieves. Addition agents can be included in the bathformulation to alter electrical conductivity and solution viscosity aswell as the composition of the film at the anode surfaces. The abovefactors are determined experimentally for each system and partconfiguration.

An electrolyte comprising a major portion of hydrofluosilicic acid and aminor portion of ethylene glycol, not including the otherabove-described additives, has also been found to be useful forthrough-etching of Be-Cu alloys and for etching Ni-Fe-P magnetic alloyfilms.

Beryllium-copper alloys have been found to be useful in the productionof substrates for electrical components. In one application, the metalsheets are suitably masked and etched through their entire thicknessesto form chainlike structures. Generally, the conventional process foraccomplishing the etching has involved exposure to aqueous chemicalsolutions, such as acidified ferric chloride or ammonium persulfate. Therate of dissolution, however, in such chemical etchants is influenced bythe concentration of the solution, the presence of dissolved coppersalts, and the temperature of the solution, as well as the degree ofagitation of the solution. Thus, in the same period of time, one partmay be etched properly and another part over-etched or under-etched dueto slight variation in conditions.

Where the part to be etched is a piece of berylliumcopper alloy which isto be etched completely through at one or more points, the part is firstprovided with a coating of a suitable masking or resist material toconfine the etching to the desired portions of the base metal. The partis then positioned between two cathodes which may be copper or stainlesssteel sheets and is connected as the anode in the system. Theelectrolyte is then introduced into the cell and an anodic currentdensity of at least 50 a.s.f. is applied.

Where the part to be etched is nickel-iron-phosphorus alloy, thepreferred electrolyte is an aqueous solution of hydrofiuosilicic acidand ethylene glycol. For this embodiment, the preferred cathode materialis stainless steel sheet or foil and the anodic current density on thepart is preferably in the range of from 500 to 2000 a.s.f.

The following two examples, Examples 2 and 3, illustrate theabove-described electrolytic etching of Be-Cu and Ni-Fe-P alloys.

EXAMPLE 2 A piece of beryllium-copper alloy 0.003 inch thick isanodically connected between two stainless steel cathodes. The sheet isprovided with resist coated areas on those portions of the surface whichare not be to etched. An anodic current density of 500 a.s.f. is appliedto the part for two minutes in an electrolyte comprising 125 ml. (30% byweight of H SiF and 25 ml. of reagent grade ethylene glycol.

There is no substantial attack on the beryllium-copper alloy in theabsence of passage of the direct current through the part.

The extent and rate of removal of the base metal is not influenced bysmall changes in solution temperature. The amount of metal removal canbe ascertained and controlled through the use of Ampere-hour meters. Therate of penetration is directly related to the current density selected.

EXAMPLE 3 A thin film of nickel-iron-phosphorus magnetic alloy wasdeposited on a palladium coated beryllium-copper alloy. Magnetic alloybits, in a density of 36 bits to a word line, were protected with aresist material. The necks between the covered or protected bits werethen etched by immersing the part as an anode in an electrolytic cellcontaining a stainless steel sheet cathode. The electrolyte contained125 ml. hydrofluosilicic acid (30% by weight H SiF and 25 ml. ethyleneglycol. An anodic current density of approximately 1000 a.s.f. wasapplied for about 40 seconds with a current of 200 milliamperes. Thetotal exposed area of a 36 bit word line is approximately 0.03 squareinch. The electrolyte temperature was maintained at from 20 to 30 C.Satisfactory etching of the necks was achieved without corrosioncracking of adjacent bit areas.

It will be apparent to those skilled in the art that various changes maybe made in the compositions and procedures described above withoutdeparting from the spirit or scope of the invention as expressed in thefollowing claims.

What is claimed is:

1. A method for smoothly etching the surface of a Be-Cu alloy partcontaining grains of cobalt beryllide comprising anodically etching saidpart in an electrolyte of the following composition:

a major portion of hydrofiuosilicic acid, as 30% by HgSiFs,

a minor portion of ethylene glycol,

a small amount of hydroxylamine hydrochloride, and

a minor portion of isopropyl alcohol containing dissolved therein asmall amount of 2,2 diquinoline.

Hydrofluosilicic acid as 30% by weight H SiF ml Hydroxylaminehydrochloride grn 0.5

Ethylene glycol ml 20 Isopropyl alcohol containing dissolved therein 0.2

gm, 2,2 diquinoline ml 25 4. The method of claim 1 wherein a currentdensity of from 500 to 1000 a.s.f. is applied to the surface of saidpart.

5. An electrolyte composition for smoothly etching a Be-Cu alloy partcontaining cobalt beryllide grains when said part is immersed as ananode in said electrolyte comprising:

a major portion of hydrofluosilicic acid, as 30% by weight H SiF a minorportion of ethylene glycol,

a minor portion of isopropyl alcohol having dissolved therein a smallamount of 2,2 diquinoline, and

a small amount of hydroxylamine hydrochloride.

6. An electrolyte as described in claim 5 wherein said hydrofluosilicicacid is on the order of about 60% by volume of said composition, saidethylene glycol is on the order of about 20% and said isopropyl alcoholis on the order of about 20% by volume.

7. An electrolyte as described in claim 5 having the followingcomposition:

Hydrofluosilicic acid as 30% by weight aqueous H SiF ml 60 Hydroxylaminehydrochloride gm 0.5 Ethylene glycol ml 20 Isopropyl alcohol containingdissolved therein 0.2

gm. 2,2 diquinoline ml 25 References Cited UNITED STATES PATENTS 2/1937Donahue -150 3/1940 Gahaean 75-150 ROBERT K. MIHALEK, Primary Examiner.

1. A METHOD FOR SMOOTHLY ETCHING THE SURFACE OF A BE-CU ALLOY PARTCONTAINING GRAINS OF COBALT BERYLIDE COMPRISING ANODICALLY ETCHING SAIDPART IN AN ELECTROLYTE OF THE FOLLOWING COMPOSITION: A MAJOR PORTION OFHYDROFLUOSILICIC ACID, AS 30% BY WEIGHT H2SIF6, A MINOR PORTION OFETHYLENE GLYCOL, A SMALL AMOUNT OF HYDROXYLAMINE HYDROCHLORIDE, AND AMINOR PORTION OF ISOPROPYL ALCOHOL CONTAINING DISSOLVED THEREIN A SMALLAMOUNT OF 2,2'' DIQUINOLINE.
 5. AN ELECTROLYTE COMPOSITION FOR SMOOTHLYETCHING A BE-CU ALLOY PART CONTAINING COBALT BERYLLIDE GRAINS WHEN SAIDPART IS IMMERSED AS AN ANODE IN SAID ELECTROLYTE COMPRISING: A MAJORPORTION OF HYDROFLUOSILICIC ACID, AS 30% BY WEIGHT H2SIF6, A MINORPORTION OF ETHYLENE GLYCOL, A MINOR PORTION OF ISOPROPYL ALCOHOL HAVINGDISSOLVED THEREIN A SMALL AMOUNT OF 2,2'' DIQUINOLINE, AND A SMALLAMOUNT OF HYDROXYLAMINE HYDROCHLORIDE.